Linear beam tube having an insulated,symmetrically located,electrode of reactive material in the collector assembly



June 3, 1969 R. E. EGGERS ET L 3,448,324

LINEAR BEAM TUBE HAVING AN INSULATED, SYMMBTRIC ALLY LOCATED, ELECTRODE 0F REACTIVE MATERIAL IN THE COLLECTOR ASSEMBLY Filed July 28, 1966 FIG 3 INVENTORS ROBERT E. EGGERS BY NORMAN H. POND ATTORNEYS United States Patent Calif.

Filed July 28, 1966, Ser. No. 568,534 Int. Cl. H01j /34 US. Cl. 315- 6 Claims ABSTRACT OF THE DISCLOSURE A collector apparatus for linear beam devices is described wherein an electrode of reactive material is symmetrically positioned at the partially open end of the collector member remote from the beam generating assembly and electrically insulated from the collector.

The present invention relates in general to electron discharge devices and more particularly to apparatus for preventing collector burn out in electron discharge devices.

Broadly stated, the present invention, to be described in greater detail below, is directed to a collector assembly for linear beam devices wherein an electrode formed of a reactive material such as titanium is located in the collector assembly for collecting and absorbing positive ions located in the collector region and particularly in the center of the electron beam.

In electron discharge devices, the beam of electrons which has been utilized to generate or amplify a radio frequency signal must be collected in a collector assembly. When the electron discharge device operates at high powers, the collection of the beam becomes a considerable problem since substantial heat is generated in the region where the beam strikes the collector and this heat must be dissipated or the electron beam will burn a hole through the collector. This problem of collector burn out becomes particularly critical in high power linear beam devices such as klystrons, traveling wave tubes and the like where the beam is maintained focused in such a small cross section area for best interaction with an R.F. wave that unless the beam is expanded it will melt the portion of the collector on which it impinges. For these situations various exotic cooling systems have been proposed to dissipate this heat.

In all of these systems heavy reliance is made upon the distribution of the electron beam over as large a surface as possible for proper heat dissipation. Typically, the space charge forces within the beam are relied upon to expand the beam in the collector region outside the focusing magnetic field which maintains the beam tightly focused during passage through the wave-beam interaction structure.

One of the problems continuously encountered in devices of this nature is the presence of positive ions created in the tube, and particularly in the collector region, as a result of gas evolution from the metal surfaces heated -by the electron beam. In the devices constructed in accordance with the prior art, these positive ions have been attracted to the center of the beam due to the negative potential of the beam and the presence of the positive ions within the beam neutralizes the beams negative potential and its otherwise normal tendency to spread after passing out of the focusing magnetic field. The end result of the existence of the positive ions is for the electron beam to remain concentrated as it passes through the collector and impinge on the surface of the collector in such a small area as to melt a hole through the collector. This phenomenon is especially true in so-called depressed collectors which are operated in potentials lower than that of the R.F. structure. In such collector assemblies it is more difficult for ions to escape from the collector end of the tube by flowing to the cathode.

In accordance with the present invention, an electrode of reactive material positioned centrally of the collector collects and absorbs the ions so that the desired beam spread results.

In accordance with another aspect of the present invention, the electrode located in the collector assembly is maintained at cathode potential or at a potential negative with respect to the collector member. With this construction, positive ions are attracted by the electrode and strike the electrode with sufiicient velocity to be permanently absorbed by the active material of the electrode. Additionally, with this construction, not only are positive ions attracted to the electrode but electrons are repelled by the electrode since the remainder of the collector surrounding the electrode is more positive and therefore more attractive to the negative charged electrons.

In accordance with another aspect of the present invention, the electrode is supported in the collector assembly on an insulator member and is thereby electrically insulated from the collector. With this construction, when the electron device is first turned on, the electrode intercepts electrons until the electrode has developed an electrostatic potential equal or close to cathode potential. After this time, operation of the electrode is essentially the same as described above in the next preceding paragraph with positive ions accelerated to and absorbed by the electrode and electrons repelled by the electrode. The ion current is constantly off-set by an equal amount of electron interception by the electrode.

The construction in accordance with the present invention not only provides protection against collector burnout, but also provides a monitor for R.F. interaction and the gas level of the device. When there is no beamwave interaction and therefore no R.F. modulation of the beam, few, if any, electrons are intercepted by the electrode so that the current flow in the electrode is due primarily to gas ions and is proportional to gas level. When beam-wave interaction takes place, electrons in the beam are accelerated and some of these accelerated electrons strike the electrode and produce a current flow opposite to that of the positive ions. This electron interception results in a reduced electrode current, and in some cases, a reversal of polarity of electrode current. This indication of beam-wave interaction is completely independent of the frequency of the R.F. wave.

Other objects and advantages of this invention will become apparent when reading the following description and referring to the accompanying drawing in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a foreshortened side elevational view partially broken away illustrating an electron discharge device constructed in accordance with the present invention;

FIG. 2 is an enlarged sectional view of a portion of the structure shown in FIG. 1 and delineated by line 22; and

FIG. 3 is a view similar to FIG. 2 and illustrating a collector assembly constructed in accordance with another aspect of the present invention.

As set forth above, the present invention is directed to a collector assembly for an electron discharge device. The invention is particularly useful in linear beam devices where the linear beam focused and directed along a straight line through the wave-beam interaction structure passes out of the structure into an assembly for collection. While the present invention will be described in detail below with particular reference to utilization in a traveling wave tube, it will be appreciated that the invention is equally applicable to other linear devices such as, for example, Klystron tubes, and can also be utilized in non-linear devices where there is a concentration of electron energy.

Referring now to the drawings, there is illustrated a traveling wave tube 11 constructed with a collector assembly in accordance with the present invention. The traveling wave tube 11 is formed with a vacuum envelope 12 provided with a beam generating assembly 13 at one end of the tube, a collector assembly 14 located at the other end of the tube and spaced from the beam generating assembly 13, and a wave-beam interaction structure 1'5 positioned between the beam generating assembly 13 and collector assembly 14 so that the beam of electrons generated in assembly 13 is directed through the interaction structure 15 for wave-beam interaction as described in detail below and for collection in the collector assembly 14. Magnet structure such as, for example, a solenoid 16, is provided around the wave-beam interaction structure for maintaining the beam focused during passage through the interaction structure 15 but permitting beam spread when the beam reaches the collector assembly 14. Other focusing arrangements such as, for example, periodic permanent magnet focusing, can be utilized.

The schematically illustrated beam generating assembly 13 includes a thermionically heated cathode 21 and a centrally apertured anode 22 with means schematically illustrated as a battery 23 for maintaining the cathode negative with respect to the anode for acceleration of electrons from the cathode 21 toward and through the apertured anode 22 and into and through the interaction structure 15.

The interaction structure 15 can be any slow or fast wave structure and is shown for illustrative purposes as a coupled cavity structure made up of cavity resonators 24 formed by partially hollowed out discs 25 located within the envelope and centrally apertured at 26 for passage of the beam axially of the tube. The discs 25 are provided with coupling irises 27 for coupling electromagnetic wave energy between cavity resonators 24. An R.F. signal input assembly such as input waveguide 28 is provided for directing a signal to be amplified to the interaction structure 15, and an output coupling assembly such as an output waveguide 29 is provided for coupling amplified wave energy from the last cavity of the interaction structure 15 to a load not shown. So that the tube canbe efliciently slidably inserted and axially positioned Within the magnet structure, the discs 25 are notchd to permit the input waveguide to run the length of the tube within the magnet structure and the connections to the input and output waveguides located close to one another.

The collector assembly 14 includes a hollow cylindrical collector member 30 of high thermal conductivity such as, for example, copper, secured to the tube at the end of the wave-beam interaction structure in a vacuum-type manner with one end 31 of member 30 open to receive the electron beam and the other end provided with a conically tapered inner surface 32 for desired spread of the electron beam over maximum surface area. The outer surface of the collector member 30 is provided with a plurality of longitudinal slots 33, the radial outward portions of which are closed by a collector sleeve such as of copper.

While the particular construction of the cooling fluid passageways in the collector does not form a part of the present invention, a typical construction will be described. Certain of the slots 33 are provided in communication with a cooling fluid input tube 35 and connected to other slots which are in communication with cooling fluid output tube 36 whereby coolant fluid such as water can be circulated through the slots 33 from input tube 35 to output tube 36 to cool the collector member and dissipate heat generated in the collector member 30 by impingement of electrons on the inner surface thereof.

The inwardly conically tapered end of the collector member 30 is centrally apertured as at 40, and an electrode member 41 of reactive material such as titanium or zirconium is located at this aperture, spaced from and electrically insulated from collector member 30. The word reactive is used to mean a material which will collect positive ions by chemical absorption or entrapment or sputter when subjected to ion bombardment and condense and entrap other ions. Other examples of reactive materials are molybdenum, chromium, tungsten, tantalum, aluminum and zirconium. In the particular embodiment of this invention illustrated in FIG. 2, electrode 41 is in the shape of a cylindrical slug rigidly and electrically connected such as by brazing to a metallic support rod 42 of a material such as copper having high heat and electrical conductivity. The other end of support rod 42 is rigidly supported in a vacuum-type manner such as by brazing to the inner flanged member 43 of a pair of concentric flanged members 43 and 44 which are secured together along mat-ing flanged portions such as by brazing. The outer flanged member 44 is supported on one end of an insulating sleeve 45 such, for example, alumina ceramic. The other end of insulating sleeve 4'5 is secured to a flange member 46 which is in turn connected via an annular ring member 47 to a metallic sleeve 48 surrounding the support rod '42 and secured to a vacuum-type manner such as by brazing to the collector member 30.

With this particular construction, the electrode 41 can be positioned at the desired location in front of aperture 40 and both cooled and connected in an electrical circuit by metallic support rod 42. As illustrated in FIG. 1, the electrode 41 can be maintained at negative potential with respect to the collector member such as by being connected via electrical circuit, schematically illustrated as conductor 49, to the cathode 21. The tube is evacuated and sealed by means of an exhaust tube (not shown). A detect-ion device such as a meter connected in conductor 49 can be provided for monitoring the operation of the tube as described in greater detail below.

Typical operation of the traveling wave tube 11 as illustrated in FIGS. 1 and 2 will now be described. When the device is turned on, a beam of electrons is generated in the beam generating assembly 13 and directed through the apertured anode 22 and the apertures in the discs 25 of the slow wave structure for interaction with a radio frequency electromagnetic wave traveling through interaction structure 15 from input waveguide 28 to output waveguide 29. The interaction circuit 15 is constructed such that energy is given up from the beam to the wave to amplify the radio frequency wave. The electron beam which has been bunched during interaction passes out through the end of the interaction structure 15 into the collector assembly 14 for impingement upon the surfaces of the collector member 30. As the beam enters the collector assembly 14, it passes out of the focusing magnetic field of solenoid 16 and due to space charge forces within the beam tends to spread and impinge upon the walls of collector member 30. As the collector member 30 heats up, gas is evolved from the metal surfaces of collector member 30 as well as from other portions of the tube. When electrons collide with these gas molecules, positive ions are created.

Due to the charge of the positive ions, they are attracted to the center of the electron beam where they would normally neutralize the negative potential of the beam if they were allowed to collect in any numbers. Instead of remaining at the center of the beam, the positive ions are attracted to the negative electrode 41 where an ion current is established in conductor 49, which current can be measured by meter 50. With positive ions removed from the electron beam, the space charge forces of the electrons cause the beam to spread and uniformly distribute over the surfaces of the collector member 30 thereby avoiding collector burn-out.

This structure not only prevents collector burn-out, but it also serves as an indication of the gas level within the tube, and a monitor for the radio frequency electromagnetic wave interaction within the tube. For example, if the tube is operating improperly, such as, if the magnetic field of the solenoid is not properly oriented with respect to the axis of the tube or the electron beam is not operated within the desired range so that the electron beam strikes a portion of the slow wave circuit or the sides of the aperture opening into the collector, the amount of gas evolved in the tube due to the heating of the normally unheated tube parts will exhibit itself by a high current reading on the meter 50. Also, if changes occur in the supply of radio frequency magnetic wave energy to the tube due to turning on the tube or to unknown circumstances external to the tube circuit, the collector construction in accordance with the present invention provides an indication of this change in RF. wave energy. The indication of such change results from the fact that when proper operating interaction is taking place within the tube between the RF. wave on the slow Wave circuit and the electron beam, certain electrons of the beam are accelerated in order to bunch the beam. Due to their increased energy, some of these accelerated electrons will strike the electrode 41 and thereby produce an electron current flow opposing positive ion current. A change in wave-beam interaction will change the electrode current or in some cases a reversal of the polarity of the current in conductor 49.

Referring now to FIG. 3, there is shown an alternative embodiment of the present invention wherein the electrode 41 is mounted such as by the intermediary of a sleeve 41" on a support rod 42 of an insulating material such as, "for example, alumina ceramic. This support rod is mountd on a metallic disc member 51 such as of copper Which is directly secured in a vacuum-type manner to the tube such as by means of a sleeve 48 surrounding the support rod 42 and electrode 41'.

When the tube incorporating electrode 41' is turned on, this electrode 41 initially intercepts electrons from the beam until a negative electrostatic potential has been developed substaintially equal to cathode potential. At this potential positive ions are accelerated toward and are buried in the electrode. After the tube has run for a short time, the electrode 41' operates in the .same manner as electrode 41 described above with reference to FIGS. 1 and 2. As more and more positive ions are absorbed, the tendency to establish a positive electrostatic potential on the electrode 41' is oit-set by an electron interception. That is, as the potential on electrode 41 become more positive, more and more electrons are intercepted and collected to reduce the potential of electrode 41' down to substantially cathode potential.

While one embodiment of this invention has been shown and described, it will be apparent that other adaptations and modifications can be made without departing from the true spirit and scope of the invention.

What is claimed:

1. In an electron discharge device having a vacuum envelope, a beam generating assembly located at one position within said envelope for directing a beam of charged particles to a collector assembly spaced therefrom and with an electromagnetic wave interaction structure located below said beam generating assembly and said collector assembly the improvement of a collector assembly including a hollow collector member open at one end to receive said beam of electrons and partially open at the other end; an electrode of reactive material and means for supporting said electrode symmetrically in said collector assembly at said partial opening in said other end of said collector and electrically insulated therefrom for collecting positive ions.

2. The structure in accordance with claim 1 characterized further in that said support means for said electrode includes a metallic electrically conductive support rod and means for providing a potential to said support rod negative with respect to collector member.

3. The device of claim 1 characterized further in that said support means for said electrode is a material of low electric conductivity whereby said electrode is insulated from said collector.

4. A linear electron discharge device having a vacuum envelope, a beam genera-ting assembly located at one end of said envelope for directing a linear beam of electrons toward a spaced location within said envelope, said beam generating assembly including a cathode and an anode and means for maintaining said cathode negative with respect to said anode; a collector assembly spaced from said beam generating assembly and adapted to receive the beam of electrons from said generating assembly; and an electromagnetic interaction structure located between said beam generating assembly and said collector assembly for providing interaction between the particles of said linear beam and a radio frequency wave travelling along such interaction structure; said collector assembly including a hollow collector member coaxial with said electromagnetic interaction structure and open at the end thereof closest the beam generating assembly to receive said beam of electrons, the other end of said collector member symmetrically centrally apertured, an electrode of reactive material, and means for supporting said electrode at the central aperture in said other end of said collector member and electrically insulated therefrom for collecting positive ions.

5. The electron discharge device in accordance with claim 4 characterized further in that said support mean-s for said electrode includes a metallic electrically conductive support rod axially aligned with said beam of electrons and means for providing cathode potential to said support rod.

6. The electron discharge device of claim 4 characterized further in that said support means for said electrode is axially aligned with said electron beam and is of a material with a low electric conductivity whereby said cathode is electrically insulated from said collector.

References Cited UNITED STATES PATENTS 12/1966 Ward et a1 315-5.38 6/1967 Yasuda et a1 315-3.5

US. Cl. X.R. 

